The Field of the Invention
Implementations described herein relate generally to microneedle electrode patches and, more particularly, to microneedle electrode patches comprising a microneedle electrode array where each of the microneedle electrodes are individually addressable via an external electronics assembly, as well as systems and methods thereof.
Related Art
Traditional nerve conduction studies are typically performed by placing two sets of large area surface electrodes on the skin overlying a nerve, one for recording and one for stimulation. In the case of motor studies, the recording electrodes are typically placed over a muscle innervated by the nerve rather than the nerve itself. Current pulses are then passed through the stimulating electrodes, leading to depolarization of underlying nerves. This depolarization propagates along the nerve in both directions. When the wave of depolarization passes through the tissue underlying the recording electrodes, the electrode records a generated voltage that then analyzed. The two measurements commonly used in traditional nerve conduction studies are the response amplitude and the conduction velocity. The response amplitude is typically reduced in cases of axonal loss. The conduction velocity is typically reduced in demyelinating disease.
Despite operator effort to place the stimulating and recording electrodes as close to the course of the target nerve as possible, anatomic variability can cause unavoidable errors in electrode positioning. With regard to the stimulating electrodes, positioning errors can cause an increase in the electrical current required to deliver an adequate stimulus to the nerve under test, leading to patient discomfort and unintentional stimulation of adjacent nerves. With regard to recording electrodes, positioning errors can cause artifacts such as baseline deflections and reduction in maximal amplitude. In clinical practice, placement errors can be minimized by using stimulus and recording sites having minimal anatomic variability and ensuring the test is conducted by a trained operator capable of recognizing placement error artifacts and adjusting electrode positions to minimize them.
An ideal set of surface stimulating electrodes should be very small and located directly over the nerve of interest, thereby delivering maximum current to the target while minimizing unintentional stimulation of the surrounding tissue. Likewise, ideal recording electrodes would be very small and located directly over the nerve of interest, thereby maximizing the signal recorded from the target while minimizing artifact produced by surrounding tissue.
Simply increasing electrode size, thereby increasing the chance that the nerve lays directly underneath some portion of the electrode, is not an effective mechanism for reducing placement error. In the case of stimulating electrodes, larger active sites typically require larger current pulses to depolarize an underlying nerve and, thus, increase unintentional stimulation of nearby tissue. In the case of recording electrodes, a larger active site does typically reduce the distance between an underlying nerve and the electrode pad, thereby increasing the signal produced by that nerve's depolarization; however, it also increases the volume of unrelated tissue lying under the pad, which will increase the recorded noise and artifact.
Conventional nerve conduction studies have typically been limited by the presence of stimulation artifacts that obscure evoked nerve and muscle signals. In practice, such stimulation artifacts can be minimized by increasing the distance between the stimulation and recording electrodes, allowing the stimulus artifact to dissipate before the evoked potential reaches the recording site. While effective, increasing the distance between the stimulation and recording electrodes makes it difficult to assess peripheral nerves over comparably short lengths and potentially reduces sensitivity. For example, a short region of conduction velocity slowing (e.g., the median nerve at the wrist, as in carpal tunnel syndrome) can be clearly seen when the stimulus and recording electrodes lie directly on either side of that region; however, if the electrodes are separated from that region by a long length of normal nerve, the net observed conduction velocity can be normal despite the disease state. Accordingly, ideal stimulating and recording electrodes should incorporate a mechanism for preventing or removing stimulation artifact, allowing stimulation and recording to occur at very close proximity to each other and enabling a wider variety of focal nerve assessment.
Accordingly, a need exists for improved devices, systems and methods for performing nerve conduction studies and related measurements.